Acyclic Secondary Amines Research Articles

Synthesis of Tetrasubstituted Enamines Using Secondary Amines and In Situ-Generated Allenes from Nitrocyclopropanes.

A novel reaction of cyclic and acyclic secondary amines with in situ-generated allene intermediate species from nitro-substituted donor-acceptor cyclopropanes is reported. In the presence of a simple inorganic base, NaOH, tetrasubstituted enamine derivatives can be obtained in moderate to excellent yields. The reaction is operationally easy, features mild reaction conditions and simple inorganic bases, and is free of transition metals.

Chiral Discrimination of Acyclic Secondary Amines by 19F NMR.

Chiral aliphatic amine compounds exhibit a range of physiological activities, making them highly sought-after in the pharmaceutical industry and biological research. One notable obstacle in studying these compounds stems from the pronounced steric hindrance surrounding the nitrogen atom. This characteristic often leads to a weak affinity of acyclic secondary amines for molecular probes, making their chiral discrimination intricate. In response to this challenge, our research has unveiled a novel 19F-labeled probe adept at recognizing and distinguishing between enantiomers of these acyclic secondary amines. By strategically incorporating a single fluorine atom as the 19F label, we have managed to diminish the steric hindrance at the binding site. This alteration bolsters the probe's affinity toward bulkier analytes. As a testament to its effectiveness, we have successfully employed our probe in the chiral analysis of relevant pharmaceuticals, accurately determining their enantiocomposition.

Visible-Light-Irradiated Multicomponent Reactions of Aliphatic Amines, Propiolate Acid Esters, and CF3 SO2 Na for Accessing β-CF3 Enamines.

A novel one-pot two-step multicomponent reaction has been achieved for the preparation of β-CF3 enamines by using different aliphatic amines, propiolates, and CF3 SO2 Na as starting material. In this protocol, various aliphatic amines including primary amines, cyclic or acyclic secondary amines were demonstrated to be good coupling partners, and different β-CF3 enamines were obtained in moderate to good yields. Among them, the primary aliphatic amines only gave pure (E)-β-CF3 enamines as products. The synthetic utility of the MCRs strategy was further demonstrated by mild conditions, gram-scale synthesis and natural sunlight-induced protocol. Preliminary mechanistic studies suggest that this trifluoromethylation of C(sp2 )-H involves radical process.

Axially Chiral N,N-Ligand-Promoted Pd-Catalyzed Enantioselective Allylic Amination and Alkylation.

An axially chiral N,N-ligand developed from a [1,1'-binaphthalene]-2,2'-diol (BINOL)-based skeleton and phenanthroline is found to be capable of promoting Pd-catalyzed asymmetric allylic amination and alkylation of allyl acetates. The reaction is compatible with cyclic and acyclic secondary amines, primary aliphatic amines, malononitrile, and dialkyl malonates, affording the corresponding chiral products in up to 99% yield and with up to >99% enantiomeric excess.

Flow Electrochemistry for the N-Nitrosation of Secondary Amines.

A flow electrochemical method towards the synthesis of N-nitroso compounds from secondary amines using cheap and readily available sodium nitrite has been developed. Sodium nitrite dissolved in aqueous acetonitrile made additional electrolytes unnecessary. This mild and straightforward approach made the use of acids or other harsh and toxic chemicals redundant. This procedure was applied to an assortment of cyclic and acyclic secondary amines (27 examples) resulting in yields of N-nitrosamines as high as 99 %. To demonstrate the practicality of the process, scaled-up reactions were performed. Finally, selected products could be purified by using an in-line acidic extraction.

Pd-Catalyzed Amination of Base-Sensitive Five-Membered Heteroaryl Halides with Aliphatic Amines.

We report a versatile and functional-group-tolerant method for the Pd-catalyzed C-N cross-coupling of five-membered heteroaryl halides with primary and secondary amines, an important but underexplored transformation. Coupling reactions of challenging, pharmaceutically relevant heteroarenes, such as 2-H-1,3-azoles, are reported in good-to-excellent yields. High-yielding coupling reactions of a wide set of five-membered heteroaryl halides with sterically demanding α-branched cyclic amines and acyclic secondary amines are reported for the first time. The key to the broad applicability of this method is the synergistic combination of (1) the moderate-strength base NaOTMS, which limits base-mediated decomposition of sensitive five-membered heteroarenes that ultimately leads to catalyst deactivation, and (2) the use of a GPhos-supported Pd catalyst, which effectively resists heteroarene-induced catalyst deactivation while promoting efficient coupling, even for challenging and sterically demanding amines. Cross-coupling reactions between a wide variety of five-membered heteroaryl halides and amines are demonstrated, including eight examples involving densely functionalized medicinal chemistry building blocks.

Catalyst-free electrochemical sulfonylation of amines with sulfonyl hydrazide in aqueous medium.

An efficient electrochemical sulfonylation of amines with sulfonyl hydrazides under exogenous-oxidant-free and catalyst-free conditions in aqueous medium was developed. A wide variety of sulfonamides were prepared via a simple electrochemical process from various cyclic or acyclic secondary amines, as well as more challenging free primary amines with equivalent amount of aryl/heteroaryl hydrazides in air under mild conditions. This protocol was found to be excellent in terms of facile scale-up, and to show great potential in the modification/synthesis of bioactive compounds. The reaction mechanism was investigated by a series of control experiments and CV studies, which indicated that the reaction might have gone through a radical pathway. Also, n-Bu4NBr served both as a supporting electrolyte and a redox agent to yield sulfonyl radical species and sulfonyl cations from sulfonyl hydrazides.

Construction of tetrasubstituted stereocenters via asymmetric catalysis using chiral acyclic secondary amines

Construction of tetrasubstituted stereocenters via asymmetric catalysis using chiral acyclic secondary amines

Metal‐Free Synthesis of S‐Aryldithiocarbamates: Aryl C−S Bond Formation at Room Temperature†

AbstractAryl halides containing electron‐withdrawing substituent(s) at ortho and para position undergoes aromatic nucleophilic substitution reaction with sulfur nucleophile present in dithiocarbamate anions at room temperature. In the present study, several cyclic and acyclic secondary amines reacted in situ with carbon disulfide to form dithiocarbamate anions, which then react with different haloarenes resulting in the formation of aryldithiocarbamates. A series of aryldithiocarbamates are obtained in high yields by this procedure.

Iodine‐Mediated sp3 C−H Amination Reactions Forming α‐Amino Ketones/Esters and Fused Imidazoles

AbstractAn iodine‐mediated direct sp3 C−H amination reaction has been established for the synthesis of nitrogen‐containing compounds from readily available substrates under transition‐metal‐free conditions. The I2‐promoted amination of ketones/esters with cyclic or acyclic secondary amines using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a base led to the formation of various α‐amino ketone or ester products including two medications, Amfepramone and Plavix. Sequential I2‐mediated sp3 C−H amination and condensation of ketones with 2‐aminopyridines in the presence of Na2CO3 produced a series of imidazo[1,2‐a]pyridines and related fused imidazoles in a one‐pot reaction. This synthetic method is operationally simple and can be conveniently conducted on a gram scale under mild reaction conditions.

Allylic C-H amination cross-coupling furnishes tertiary amines by electrophilic metal catalysis.

Intermolecular cross-coupling of terminal olefins with secondary amines to form complex tertiary amines-a common motif in pharmaceuticals-remains a major challenge in chemical synthesis. Basic amine nucleophiles in nondirected, electrophilic metal-catalyzed aminations tend to bind to and thereby inhibit metal catalysts. We reasoned that an autoregulatory mechanism coupling the release of amine nucleophiles with catalyst turnover could enable functionalization without inhibiting metal-mediated heterolytic carbon-hydrogen cleavage. Here, we report a palladium(II)-catalyzed allylic carbon-hydrogen amination cross-coupling using this strategy, featuring 48 cyclic and acyclic secondary amines (10 pharmaceutically relevant cores) and 34 terminal olefins (bearing electrophilic functionality) to furnish 81 tertiary allylic amines, including 12 drug compounds and 10 complex drug derivatives, with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z).

Pd-Catalyzed Alkene Diamination Reactions with O-Benzoylhydroxylamine Electrophiles: Evidence Supporting a Pd(II/IV) Catalytic Cycle, the Role of 2,4-Pentanedione Derivatives as Ligands, and Expanded Substrate Scope.

This article describes continued studies on Pd-catalyzed alkene diamination reactions between N-allylguanidines or ureas and O-benzoylhydroxylamine derivatives, which serve as N-centered electrophiles. The transformations generate cyclic guanidines and ureas bearing dialkylaminomethyl groups in moderate to good yield. We describe new mechanistic experiments that have led to a revised mechanistic hypothesis that involves a key oxidative addition of the electrophile to a PdII complex, followed by reductive elimination from PdIV to form the alkyl carbon-nitrogen bond. In addition, we demonstrate that acac, not phosphine, serves as a key ligand for palladium. Moreover, simple acac derivatives bearing substituted aryl groups outperform acac in the catalytic reactions, and phosphines inhibit catalysis in many cases. These discoveries have led to a significant expansion in the scope of this chemistry, which now allows for the coupling of a variety of cyclic amines, acyclic secondary amines, and primary amines. In addition, we also demonstrate that these new conditions allow for the use of amide nucleophiles, in addition to guanidines and ureas.

Iodine mediated direct coupling of benzylic alcohols with dithiocarbamate anions: An easy access of S-benzyl dithiocarbamate esters under neat reaction condition

An efficient, metal and solvent free synthesis of S-benzylic dithiocarbamate esters has been demonstrated via the iodine mediated direct C-S coupling of benzylic alcohols with dithiocarbamate anions generated in-situ by the reactions of amines and carbon disulphide. All the reactions were very fast (15–30 min) and performed under open air atmosphere. Cyclic and acyclic secondary amines, primary amine, aromatic amine actively participated in the one-pot coupling reactions with different benzylic alcohols. Non benzylic alcohols offer the synthesis of O-thiocarbamate compounds under the identical reaction condition.

Using the Competing Enantioselective Conversion Method to Assign the Absolute Configuration of Cyclic Amines with Bode's Acylation Reagents.

The competing enantioselective conversion (CEC) method is a quick and reliable means to determine absolute configuration. Previously, Bode's chiral acylated hydroxamic acids were used to determine the stereochemistry of primary amines, as well as cyclic and acyclic secondary amines. The enantioselective acylation has been evaluated for 4-, 5-, and 6-membered cyclic secondary amines, including medicinally relevant compounds. The limitations of the method were studied through computational analysis and experimental results. Piperidines with substituents at the 2-position did not behave well unless the axial conformer was energetically accessible, which is consistent with the transition state geometries proposed by Bode and Kozlowski. Control experiments were performed to investigate the cause of degrading selectivity under the CEC reaction conditions. The present study expands the scope of the CEC method for secondary amines and provides a better understanding of the reaction profile.

α-amination reaction of different ketones mediated by carbohydrate Cu2+ complexes

The α-amination reaction of ketones was studied and the reaction conditions were analysed by green metrics. Propiophenone and two aliphatic ketones, saturated cyclic and acyclic secondary amines were used, carbohydrate Cu2+ complexes were the catalysts to obtain the brominate intermediates. Traditional stirring and ultrasound methods were compared. The use of α-CDCuBr2 complex in the presence of propiophenone, morpholine and O2 was the best condition to carry out the α-amination reaction using a One Pot synthesis, with an 80 % yield of product isolated and no by-product was detected.

Zwitterionic Ring-Opened Oxyphosphonium Species from the Ph3P-I2 Mediated Reactions of Benzo[d]oxazol-2(3H)-ones with Secondary Amines.

Instead of the expected substituted 2-aminobenzo[d]oxazoles, relatively stable ring-opened oxyphosphonium betaines were isolated for the first time from the Ph3P-I2-mediated reactions of benzo[d]oxazol-2(3H)-ones with acyclic secondary amines. The structure of one of these compounds was unambiguously confirmed by single-crystal X-ray analysis. Thermolysis of the betaines gave rise to 2-dialkylaminobenzoxazoles with concomitant loss of triphenylphosphine oxide, suggesting their possible role as intermediates in an alternative reaction path.

Synthesis of 3-(Dialkylamino)-4-halofuro[3,4-c]pyridin-1(3H)-ones

The reaction of 4-halo-3-hydroxyfuro[3,4-c]pyridin-1(3H)-ones with acyclic and alicyclic secondary amines in ethyl acetate afforded the corresponding 3-(dialkylamino)-4-halofuro[3,4-c]pyridin-1(3H)-ones in a few minutes.

Expanding the Scope of Asinger Chemistry towards Enantiomerically Pure Secondary Amines and β-Aminothiols through Chemoenzymatic Derivatization of 3-Thiazolines

A proof of concept for a novel approach towards enantiomerically highly enriched acyclic secondary amines and β-aminothiols as non-cyclic target molecules when starting from 3-thiazolines as heterocycles is presented. Starting from 2,2,4,5,5-pentamethyl-3-thiazoline, we demonstrated this chemoenzymatic pathway to both of these types of amine molecules, which were isolated as urea derivatives with a non-optimized yield of up to 20%. As a substrate, 2,2,4,5,5-pentamethyl-3-thiazolidine, which was obtained with an enantiomeric excess (ee) of 99% in a biotransformation from the corresponding 3-thiazoline according to a recently developed protocol, was used. For the reductive desulfurization of this substrate leading to a sulfur-free secondary amine, in situ formed Ni2B turned out to be a suitable reducing reagent. However, when using lithium aluminum hydride as a reducing agent, β-aminothiol was obtained.

Synthesis of some alkylaminothiophene derivatives from 3,4-dibromothiophene and their theoretical calculations

In this study, the copper catalyzed amination reactions of 3,4-dibromothiophene with some primary, cyclic and acyclic secondary amines were investigated to prepare novel electron rich-thiophenes which are expected to be used as novel N-containing donor type monomer candidates for conductive polymers. In order to obtain better yields, this SNAr type amination reaction was optimized by studying the reaction conditions, such as the copper catalyst, the type of copper source, the presence of a base and the type of the solvent on the model reaction between 3,4-dibromothiophene and n-butylamine. A variety of 3,4-(N,N′-dialkylamino)thiophenes and 3-(N-alkylamino)thiophenes were synthesized in moderate yields under the optimized reaction conditions. In addition, two new heterocyclothiophene derivatives were successfully prepared from the cyclization reaction of 3,4-bis(N-butylamino)thiophene. The characterization of the isolated alkylaminothiophenes was performed by FTIR, 1H and 13C NMR, GCMS and elemental analysis. The theoretical calculations for all alkylaminothiophenes were executed by using the DFT/B3LYP/6-311+G(2d,p) approach.

Acceptorless Amine Dehydrogenation and Transamination Using Pd-Doped Hydrotalcites

The acceptorless dehydrogenation of acyclic secondary amines is a highly desirable but still elusive catalytic process. Here we report the synthesis, characterization, and activity of Pd-doped hydrotalcites (Pd-HTs) for acceptorless dehydrogenation of both primary and secondary amines (cyclic and acyclic). These multifunctional catalysts comprise Bronsted basic and Lewis acidic surface sites that stabilize Pd in 0, 2+, and 4+ oxidation states. Pd speciation and corresponding catalytic performance is a strong function of metal loading. High activity is observed for the dehydrogenation of secondary aliphatic amines to imines, and N-heterocycles, such as indoline, 1,2,3,4-tetrahydroquinoline, and piperidine, to aromatic compounds. Oxidative transamination of primary amines is achieved using low Pd loading (0.5 mol %), without the need for oxidants. The relative yields of secondary imines afforded are consistent with trends for calculated free energy of reaction, while yields for transamination products corre...